Control devices

ABSTRACT

A control device suitable for the fuel injection pump of an internal combustion engine is shown. The device comprises a rotatable cam having a plurality of symmetrical lobes and a cam follower having two rollers which are both in contact with the cam face. The cam follower is linked to an operating member of an associated pump. The rollers of the cam follower are relatively large to withstand the forces produced at high speed and the pivot for the cam follower is arranged so that it does not obstruct the space between the two rollers. The cam profile is so shaped that the two rollers are both always in contact with the surface of the cam so that there is no play in their movement.

ilnited States Patent 1191 11 3,73&1@ Sola 1 June 12, 11973 CONTROLDEVICES 3,262,715 7/1966 Abbott 280/111 [75] Inventor: Giuseppe Sola,Turin, Italy Primary Examiner-Charles J. Myhre [73] Assignees: FiatSocIeta per Aziom, Turin, Italy Assistant Examiner wesley S. R tliff In22 Filed; May 2 197 Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak[21] Appl. No.: 147,118 [57] ABSTRACT [30] Foreign Application Prioritya A control device suitable forthe fuel injection pump of S t 15 1970 It1 70096 A 70 an mternal combustlon engine 1s shown. The device ep aycomprises a rotatable cam having a plurality of symmetrical lobes and acam follower having two rollers [22] which are both in Contact with thecam face The Cam 280/ follower is linked to an operating member of anassoci- 1 0 {23/139 k ated pump. The rollers of the cam follower arerelatively large to withstand the forces produced at high speed and thepivot for the cam follower is arranged so [56] References Cited that itdoes not obstruct the space between the two roll- UNITED STATES PATENTSers. The cam profile is so shaped that the two rollers are 3,263,5128/1966 Handley 74/569 both always in contact with the surface of the camso 1,198,283 9/1916 Shira 74/53 that there is no in their movement;1,777,179 9/1930 Perlman 74/53 1,630,273 5/1927 Nordwick 74/53 14Claims, 9 Drawing Figures Ill.

Pmmcnm mama sim a w W wmiam PATENTED J!!!" 2 W3 SHEEHMF? PAIENIEIJ JUN 12 am I SHEEISBF? SJSBJBO PAIlENImJvmm mun CONTROL DEVICES BACKGROUND OFTHE INVENTION The present invention relates to a control device for apump, such as a fuel injection pump for a multicylinder internalcombustion engine. In particular, the invention relates to a controldevice of the type comprising a cam profile having a plurality ofsubstantially symmetrical lobes, extending radially outwardly in asingle plane perpendicular to the axis of rotation of the cam, and a camfollower having a pair of rollers or sliding blocks supported by arocker arm, both rollers being engaged on respective opposed lobe facesof the cam. One roller or sliding block is directly associated with anoperative element of the associated pump and is moved by the cam toproduce a pumping stroke of this operative element and the other rolleror sliding block operates as a return element to effect the returnstroke of the operative element of the pump.

This general type of control device is already known in itself and formsthe subject of other patents, such as Italian Pat. No. 759,541 andItalian Pat. No. 818,422, both in the name of the present Applicants.

It has been found that in cases where the control cam has to have fiveor more lobes, that is for the control of pumps to supply engines offive or more cylinders, there are constructional difficulties which mustbe overcome in order to achieve satisfactory functioning of thesedevices. With cams of five or more lobes the angle subtended at thecenter of the cam by each lobe is relatively small, with the result thatthe distance between the rollers which are arranged to engage with theflanks of the cam lobes also becomes rather small. In thesecircumstances there is not sufficient space between the two rollers tolocate the pivot pin on which the rocker arm which supports the rollersis mounted.

A reduction in the diameter of the pivot pin on which the rocker arm ismounted is not possible because this pin has to be sufficiently robustto resist the stresses during operation of the pump. The forces borne bythis pin are very great due to the fact that the rate of injectionnecessary for directinjection engines of high specific power and highrate of rotation, generates maximum injection pressures which increasein proportion to the rate of rotation, such pressures, in the neighborhood of the pumping chamber may frequently be as much as 800 kglcmMoreover, it is similarly not possible to reduce the diameter of therollers carried by the rocker arm to make more space because these haveto closely follow the profiles of the cam lobes, and the load on theserollers is also high. This load can reach, for example, 700 kgs on themain roller connected to the pumping element. From this it follows thatthe diameter, especially the diameter of the main roller, cannot bereduced, partly because it is necessary to keep the specific contactpressures within certain limits on the flanks of the cam lobes, andpartly because, with the heavy load and with a high rate of rotation ofthe rollers, it is necessary to interpose a floating bush between theroller and it mounting pin.

Even the solution proposed in the above mentioned Italian Pat. No.818,422 by the same Applicant, of eliminating one roller, that is thepump return roller,

. and of substituting for it a sliding block, has not provedsatisfactory in practice in the case of a cam having five or more thanfive lobes. This is because it is necessary to eliminate the wear on thecam caused by the sliding friction between such a block and the flanksof the lobes during the periods of the reciprocating action of therocker in which the negative inertia forces of the whole system whichcause the return action of the pump are opposed by the sliding block andthe cam lobe with which it is in contact. Because of these forces theend of the rocker arm, opposite that which is associated with theoperative element of the pump, is pressed against the flanks of the camlobes with such loads as to make it absolutely necessary to minimize thefriction on the lobe. This can only be achieved by the use of a rollerrather than a sliding block in this position. In brief, it is essentialto have rolling contact rather than sliding contact even between the twoelements which are subject to the least loads because these loads arenevertheless great enough to cause an undesirable amount of wear on thecam if sliding contact is used.

Moreover, in practice, such control devices for injection pumps designedto control engines of six or more cylinders, which have been designedaccording to known criteria, have had disadvantages in regard to theprofile of the cam lobes, the number of which is equal to the number ofcylinders of the engine for which the pump is intended. Thesedisadvantages arise mainly because, in order to achieve a satisfactoryrate of fuel injection the radii of the cam profiles for each lobe areextremely small and difficult to manufacture with normal mechanicalmachining techniques. These profiles also allow some slackness of theoperative element of the pump in relation to the control and returnrollers, particularly at the acceleration reversal points of the pumpingelement and hence at the reversal points of the inertia forces.

OBJECTS OF THE INVENTION It is an object of this invention to provide asolution to the problem of mounting the rocker arm member which willallow it to support rollers, both for control and return of the pumpingelement, of a sufficiently large diameter to bear the specific contactpressures upon the profile of the cam.

It is another object of this invention to provide a cam profile suitablefor guiding rollers without any slack points and which can be readilymanufactured using normal mechanical machining techniques.

SUMMARY OF THE INVENTION According to the present invention there isprovided a control device for a fuel injection pump of a multicylinderinternal combustion engine, of the kind having a cam with a plurality oflobes each lobe being symmetric about a radial line through the top deadcenter of the lobe,'a cam follower having two rollers both in contactwith the profile of the cam, the rollers being mounted-at respectiveends of a rocker arm which is supported for pivotal movement about anintermediate point midway between the roller axes to a support memberattachable to the casing of an associated pump, one of the two rollersbeing connectable by means of a connecting rod, to an operating memberof an associated pump, in which the pivotal support for the said rockerarm does not extend into the region between the two rollers, and inwhich the part of the profile of each lobe of the cam between the topdead center position and the half lift position of the cam follower isdetermined to be the appropriate envelope of the successive positions ofthe one roller when the other roller moves over the part of the profileof the cam between the bottom dead center position and the half liftposition of the said cam follower.

It will be appreciated that devices constructed in accordance with thisinvention should find particular utility in operating the pumpingelements of injection pumps having six or more lobes, that is forengines of six or more cylinders.

Various further features and advantages of the invention will becomeapparent from a consideration of the following description, withreference to the accompanying drawings, which is presented by way ofnonrestrictive example.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic side view,partially cut away, of part of a pump having a control deviceconstructed according to the invention;

FIG. 2 is a section taken along the line lI-II of FIG. 1, illustratingparticularly the assembly of the rocker cam pivot pins;

FIG. 3 is a section taken along the line III-III of FIG.

FIG. 4 is an enlarged perspective view of a rocker arm and supportsuitable for use in embodiments of the invention;

FIG. 5 is a diagram illustrating the position of the rollers and of therocker arm pivot pins in relation to a cam with five lobes, and to a camwith six lobes;

FIG. 6 is a qualitative diagram of the rate of motion of a cam followerwith respect to the cam profile according to the invention;

FIG. 7 is an enlarged diagrammatic view of part of the cam profileshowing the main and reversal rollers of the pumping element in a firstposition corresponding to the half lift position of the cam followeralong the stroke of the pumping element;

FIG. 8 is a diagrammatic view of the cam profile with the control andreverse rollers of the pumping element in a second position, againcorresponding to the half lift position of the cam follower along thestroke of the pumping element; and

FIG. 9 is an enlarged diagrammatic view of the cam profile showing theposition corresponding to the bottom dead center position of the camfollower.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In all the Figures referred toabove, the elements which correspond with each other are indicated withthe same reference numbers. Referring now to FIG. 1 there is shown thelower part 1 of a single pumping element of an injection pump controlledby a cam 2 with six equal lobes, each lobe having respective flanks 3and 3a on either side of a lobe peak B, the profiles 3 and 3a beingsymmetrical about a radial line AB from the axis A of rotation of thecam to the peak B.

The cam 2 is borne on a sleeve 4 which is driven by a shaft 5 via a clawclutch 6, which may, for example, be helicoidal, to allow for adjustmentof the angular position of the cam 2 in relation to the control shaft 5.Upon the periphery of the cam 2 there rest two rollers,

-7 and 8 respectively, mounted for rotation upon axles 9 and 10 of axes,D and E respectively, of which are parallel to the axis A of the shaft 5and supported by a rocker arm 11 which in its turn is pivotally mountedupon a support. The rocker arm 11 is mounted for pivoting movement aboutan axis 9. The support 12, together with the casing 13, forms the upperclosure of the casing of the pump 14. Between the roller 7 and its axle8 there is inserted a floating bush 15.

The connection between the roller 7 and the pumping element 1, as canalso be seen in FIG. 3, is achieved by means of connecting rods 16 andwhich are joined, at one end, to the axle 9 of the roller 7 and at theother end to a pin 17 which joins them to a cursor 18, which in itsturn, is connected to a mushroom head 19 of the pumping element 1. Themushroom head 19 is located in a groove 200 of the cursor 18 so as toallow for possible rotation of the pumping element 1 in relation to thecursor l8, and so as to maintain a rigid axial coupling with the cursor18.

With particular reference to FIG. 4, the structure of the rocker arm 11and of the related support member 12 by means of which it is attached tothe casing of the pump14 will be described.

As can be seen from FIG. 4 the rocker arm 11 comprises two generallyplate-like elements 20 and 20a, spaced from each other by a distancewhich is equal at least to the length of the rollers 7 and 8; theseelements 20 and 20a, are shaped in the form of an isosceles trianglewith rounded vertices, and are rigidly connected by a bridge 21 whichleaves sufficient space free between the elements 20 and 20a for therollers 7 and 8 to be housed. The rollers 7 and 8 are mounted on axles 9and 10 which are inserted into the holes 22-22:: and 23-2311 (the latternot visible in FIG. 4).

On the outer facing wall of each plate 20 and 20a there is a stub shaftor pin 24 and 24a, aligned with each other and with the axis G aboutwhich the rocker arm 11 is pivoted. As can be seen from the structuralarrangement described above, the rocker arm 11 can carry two rollers 7and 8 of a diameter which is large enough to bear the high pressures onthe profile of the cam, and at the same time allows the use of pivotpins 24 and 24a which, while not interfering with the rollers 7 and 8,can nevertheless be of dimensions sufficient to increase to asatisfactory degree their resistance to the fatigue strains of therocker arm during operation under heavy loads (more than 700 kgs), whichloads are transmitted from the pumping element chamber on to the main orcontrol roller 7.

The rocker arm 11, as can be seen from both FIG. 2 and FIG. 4, issupported for pivoting motion about the axis G, by a support member 12which comprises a substantially U shaped element with a base 25, andlimbs 26 and 26a. On the limbs 26 and 26a there are provided apertures27 and 27a through the faces thereof and each aperture has an opening 28and 28a. The diameter of the apertures 27 and 27a is greater than thediameter of the stub shafts or pins 24 and 24a, and the port of theopenings 28 and 28a is only very slightly greater than the diameter ofthe said stub shafts or pins. This allows the rocker arm to be assembledby inserting the pin stubs 24 and 24a radially through openings 28 and28a, and subsequently sliding the bushes 29 and 29a over the stub shaftsor pins 24 and 24a and into the apertures 27 and 27a to hold the stubshafts and hence the rocker arm 11 in position. These bushes 29 and 29awhose outer diameter matches the inner diameter of the apertures 27 and27a, prevent the rocker arm from slipping out of its supports.

The center portion, or base is provided with a collar having a centralbore 31 through which passes the sliding block 18 connected to thepumping element 1. The base 25 is moreover provided with a projectingtongue 32, to assist in locating and securing the support member 12 inthe upper part of the casing of the pump 14. This can be effectedbecause the base 25 and the tongue 32 are provided with holes 33 and 34respectively for receiving screws 35 and 36 (see FIG. 1) by means ofwhich the support 12 with the rocker arm 11 mounted on to it, can beattached to the casing 13 of the pump 14.

It will be understood, from the description above, that the structurealso allows simple assembly and disassembly of the rocker arm and of therollers so-that it is possible to replace the latter by others ofgreater or smaller diameter to compensate for possible differences dueto working and/or to wear, without having to touch the cam 2. This hasthe advantage of not changing the phasing of the cam 2 duringmaintenance operations on the pump when it is assembled on an engine.

With reference now to FIG. 5 it will be possible to appreciate theimportance of the technical problem resolved by the structure of therocker arm described above. The base diameter of the cam 2, is indicatedDb and its outer diameter is indicated De. The lift of the cam, that isthe stroke which the pumping element 1 has to make is indicated h. Thegreater the number of cylinders of the engine to be supplied, thegreater the number of lobes on the cam 2, each of which controls thepumping element 1. Since, as has already been stated, the pressureexerted by the roller 7 upon the profile of the cam is very great, thediameter of the roller 7 and hence also of the roller 8 must be above acertain minimum value and, since it is necessary to have two rollers (ashas been shown above) with a cam with six lobes, it is impossible toassemble the rocker arm 11 on a pivot pin such as 24b, which issufficiently strong if this has to pass into the zone between therollers 7 and 8, as in known control devices of this type.

As is seen in FIG. 5 in fact, in the case of a six lobe cam, the anglea, subtended at the center of the cam by each lobe, is only 60". Since,when a roller is in a position corresponding to the bottom dead centerof the cam profile, the other roller will have to be in a positioncorresponding to the upper dead center, the angle 3, subtended at thecenter A of the cam between the axes D and E of the roller will be equalto a/2. The distance ED between the centers of the two rollers will begiven by:

ED 2 AD. sin [3/2 and since the diameters of the two rollers 7 and 8must be substantially equal, the distance ED can only be slightlygreater than the diameter of the roller 7 or 8.

Therefore, as has been said already, there would be so little space freebetween the two rollers 7 and 8 of the rocker arm 11 as to make itimpossible to arrange for a pivot pin such as 24b to pass through therocker 11 in the known way and still have sufficient strength in itscenter portion to withstand the stresses caused by the heavy loadsdiscussed above.

It works out moreover, still with reference to FIG. 5, that with a sixlobe cam, since the stroke h of the pump ing element is equal to (D, Deven if relatively large base diameters Db as much as l4.h are used andhence external diameters De l5.h, the distance ED between the centers ofthe two rollers remains so small that it prevents the use of a pivot pinpassing through the rocker arm 111.

In the case of a rocker arm for a 5 lobe cam where the angle BlZ wouldbe greater by 3 than [3/2 used in the calculation of ED, (see FIG. 5),especially if rollers of relatively large diameter in relation to thediameter of the cam are used, the same problem of the impossibility offitting in a strong pivot pin is found. The problem remains,notwithstanding the apparent greater separation of the axes of therollers (from E to E and from D to D) with only five lobes, because ofthe larger angular sector available for the development of each lobe (72instead of 60) because it is preferable, if possible, to reduce the basediameter Db of the cam and consequently the distance E'D remains small.

If now a cam with eight lobes is considered, still with reference toFIG. 5, the centers of the rollers 7 8 will be at E" and D" and theangle 3/2 is reduced to B/2 =1 1.l5. The distance E"D between therollers 7 and 8 is also reduced and the problem of the pivot pin 24b iseven more serious. On the other hand, if rollers 7 and 8 of a greatlyreduced diameter were used, then because of the small difference inlength between AD and AG, it would be the passage of the peak A of thelobes (of diameter De)close to the pin 24b, which would impose arestriction on the diameter of the said pin 24b.

With the technical solution offered by this invention which allowselimination of the pivot pin in the center portion of the rocker arm, asdescribed above, the use of two rollers of large diameter is possible.

In particular, with the technical solution offered by this invention,the outer diameter of the roller 7 which controls the working stroke ofthe pumping element 1,

being independent of the pivot pin 24b of the rocker arm, may be largeenough to be able to sustain the heavy loads which are caused by highinjection pressures, and to be able to attain a high rotational speed.

With reference now to the FIG. 6, 7, 8 and 9, there will be describedthe new cam profile which allows effective utilization of the rollers 7and 8 of the rocker arm with a relatively large diameter in relation tothe base diameter Db of the cam 2. As is known, the working stroke ofthe pumping element 1 (in the direction of the arrow F in FIG. l) iseffected up to the half stroke position, by the profile of the lobes.Thus starting with the roller 7 at the position corresponding to bottomdead center of the element 1 at the base diameter Db of the cam, andmoving up to the point m (see particularly FIG. 8) of the flank of thelobe causes the element 1 to effect a half stroke (h/2) after a rotationof the cam 2 equal to 360/4n, where n is the number of lobes of the cam.

It is considered preferable to determine the profile of the lobes byinitially defining the first portion of the flank which, together withthe roller 7, generates the first half stroke h/2 and subsequently toform the second part of the profile of the lobes up to the top deadcenter (p.m.s.) by envelopement, that is by defining the second part ofthe profile to be the appropriate envelope of the successive positionsof one roller when the other roller moves over the first part of theprofile. Since the profiles 3 and 3a of the cam 2 are symmetrical inrelation to the radial line AB (see FIG. l) the cam having to serve bothfor right hand and for the left hand rotation, once the first section ofprofile up to the point m of FIG. 8, representing half the stroke h ofthe pumping element, has been defined, the remaining portion of theprofile up to the top dead center can be made by envelopement of thesuccessive positions of the roller 7 with respect to the correspondingpositions of the roller 6 during the movement of the roller 7 over thefirst section of the profile.

In this way, at the half stroke h/2 of the pumping element 1 the playbetween the two rollers 7 and 8 on the opposite flanks of the cam lobesworks out theoretically at nil. This condition is very important in thatit is precisely in this position that accelerations and hence the forcesof inertia invert, passing over from positive to negative on eachroller.

Moreover in order to obtain a good combustion in engines which requiredeliveries of fuel at up to 200 mm and more for each cycle and withtheoretical gradients of fuel delivery of the pumping element up to 45mm per degree of rotation of the shaft of the pump, it is necessary tostabilize the maximum stroke h of the pumping element 1, if possible, tokeep it below the ratio d/c 2 where d is the diameter of the pumpingelement and c is its stroke.

If pumping elements of a relatively large diameter d are avoided, thenit will be possible to contain the specific contact pressures betweenthe roller 7 and the flanks of the cam lobes within values comensuratewith a relatively long working life. Hence it is important, indetermining the profile of the cam lobes, to ensure the desired rate ofinjection without having to have recourse to the use of pumping elementshaving an excessively large diameter d.

In order to ensure a good fuel injection rate whatever the velocitygradient transmitted by the cam 2 to the pumping element 1 it is,moreover, important that the maximum speed of the element 1 should occurabout the half stroke h/2 of the said pumping element, this being theposition which also corresponds to half of the angle 3 subtended by thelobe at the center of the cam, that is the position of the rollers shownin FIG. 8.

The profile P of the upper part of the flanks of the lobes, determinedby envelopement from the contact of the main roller 7 upon the profileof the lower part P through the angular movement of the rocker arm 11and of the secondary roller 8, is thus suitable to sustain the heavyloads due to the pumping element 1.

The technical solution of the present invention also takes into accountthe kinematic determining condition according to which it is only afterthe half stroke h/2 of the pumping element 1 has been passed thatdeceleration and hence a reduction in the linear velocity of the pumpingelement commences. The dynamic conditions due to the inversion of thedirection of acceleration and hence of the forces of inertia, impose thenecessity that in proximity to the position m of the rollers on theflanks of the lobes which corresponds to the half stroke position of thepumping element there shall be the least possible play between therollers 7, 8 and the flanks of the cam lobes over which they move.

In order to take into account all these conditions, on the first part I,of the profile of the lobe the characteristics of this part of theprofile are arranged, so that the second part P of the profile of thelobe, made by envelopement from the first part P is of convex curvature,of variable radius, and has from the half stroke to about three-fourthsof the whole stroke a curve of radii about half of the diameter of theroller 7 and around five-sixths of the stroke, has a curve of radiiabout onethird of the diameter of the roller. At approximatelynine-tenths of the total stroke the curve may be reduced to radii equalto or slightly less than one-fourth of the diameter of the rollers. Atthe peaks of the lobes the curve does not go down to radii less thanone-fifth of the diameter of the rollers.

Thus the stroke h of the pumping element can be used up to percentwithout altering the rate of injection and without other disadvantages.

This condition, moreover, together with the high initial velocity givento the pumping element 1 at the beginning of the delivery phase(corresponding to the lower part of each lobe P and together with thehigh average velocity maintained during the whole injection phase, makespossible the use of pumping element diameters relatively small inrelation to the whole delivery of the pump. This is a considerableadvantage, particularly with respect to the rate of injection whichexists at the outlet of the holes of the injector (not shown).

With particular reference to FIGS. 7 and 9 it will be noted that theinitial profile P. of the lobes, has a concave curve with a radius Rmbetween 35 and 45 mm depending on the diameter chosen for the mainroller and on the desired initial velocity of the pump element. Moreparticularly the initial profile P from the bottom dead center up to thehalf stroke position h/2, comprises a first substantially rectilinearsection r coinciding with the said curve c of radius Rm terminating atthe point corresponding to approximately A h, and a third section r alsorectilinear and tangential to the intermediate section curve c andextending to the point m corresponding to the half stroke position h/2.The remainder of the profile, that is the final profile P of the lobe,from the half stroke position h/ 2, up to the top dead center at thepeak of the lobe is formed by envelopement of the initial profile P,, ashas been discussed above.

The characteristics mentioned are illustrated also in FIG. 6 withreference to the rate of motion in the case of cams of five to eightlobes. Upon the abscissa are recorded the degrees of rotation of the camfrom the bottom dead center and upon the ordinate the correspondingvalues of the fraction of a stroke h moved by the pumping element. Ascan be seen, in the region of the first half stroke the section ofrectilinear profile of rl occupies an angle of cam rotation between 2and 4, the concave curved section 0 of radius Rm which extends to theposition h/4, occupies an angle between 7 and 9, whilst the thirdsection r2, which is also rectilinear and which extends to the positionh/2, occupies the remaining 34. The gradient of third section r2,between the positions corresponding to Ah and Ah, may have a slope ofbetween 0.5 and 0.30 mm per degree of rotation of the cam.Alternatively, it can be defined in such a way that, with the pumpingelement 1 having its diameter (I no greater than twice the stroke h, atheoretical gradient of fuel delivery of the pumping element of between30 and 45 mm per degree of rotation of the cam is obtained.

From the above data it will be seen that for a 5 lobe cam there could beselected, for example, the angles 5 8.30' 4.30 18 (corresponding to13605) whilst for the 8 lobe cam there could be selected respectivelythe angles 2 7.15' 2 11.l5.

In certain cases, according to one variant of the invention, which isespecially useful for an eight lobe stroke, there can be eliminated thefirst rectilinear section r1 from the bottom dead center, whilst stillretaining the said second and third section, and r2 respectively.

What is claimed is:

l. A control device for a fuel injection pump of a multi-cylinderinternal combustion engine, said control device having a casing, a camrotatably mounted in the casing,

said cam having a surface including a plurality of lobes, each said lobebeing symmetric about a radial line passing through the top dead centerof said lobe,

cam follower means comprising a rocker arm having at each end thereof aroller, said rollers both being in contact with the surface of said cam,

a support member attached to the casing support means on said rocker armcooperating with said support member to support said rocker arm forpivotal movement about an axis intermediate said rollers, said supportmeans being outside the region between said rollers and a connecting rodhaving one end operatively connected to one of said rollers and theother end connected to a cursor slidable in said support members, saidcam surface being shaped such that the part of the profile of each lobeof said cam between the top dead center position and the half liftposition of said cam follower is determined to be the appropriateenvelope of the successive positions of said roller when the other saidroller moves over the part of the profile of said cam between the bottomdead center position and said half lift position of said cam follower.

2. The device of claim 1, wherein said rocker arm comprises twoplate-like elements, each said plate-like element having substantiallythe form of an isosceles triangle with rounded vertices and with a baselonger than the sides, a bridge element rigidly connecting saidplate-like elements side by side at the vortex opposite said base, saidsupport means including a stub shaft projecting outwardly from each ofsaid plate-like elements, means forming axially aligned apertures ineach pair of the other rounded vertices of the plate-like elements anaxle means for said rollers disposed in said apertures.

3. The device of claim 2 wherein said support member for said rocker armcomprises a substantially U- shaped element having in each limb thereofa circular aperture of diameter larger than the diameter of each saidstub shaft,

a slot in each limb of the U-shaped element, each said aperturecommunicating laterally with a respective said slot so as to provide apassage of width at least equal to the diameter of each said stubshaft'to allow the radial introduction thereof into said aperture,

a bush in each said aperture having an external diameter equal to thediameter of the respective aperture, said bush arranged for insertioninto said aperture over said stub shaft, said bush serving to lock eachsaid stub shaft in position in said aperture.

4. The device of claim 3 wherein the base of said U- shaped element hasan aperture surrounded by a collar through which said cursor passes.

5. The device of claim 2 wherein there is provided a bush between eachaxle for said rollers and the respec tive apertures in the ends of saidrocker arm.

6. The device of claim 1 wherein said cam has five or more lobes, andwherein a first part of said profile of each lobe, from the bottom deadcenter position up to the point corresponding with the half liftposition of said cam follower means, comprises a concave curve having aradius between 35 and 45 mm, and at least one rectilinear sectionbetween said point corresponding to said half lift position of said camfollower and said concave curved section to which it is tangential, saidrectilinear section extending to a point which corresponds substantiallyto a quarter of the lift of said cam follower means.

7. The device of claim 6, wherein said first portion of said profile ofeach said lobe comprises a first rectilinear section, said concavecurved section with radius between 35 and 45 mm, and a secondrectilinear section formed by said rectilinear section extending to saidhalf lift position of said cam follower means, both of said rectilinearsections being tangential to said curved section.

8. The device of claim 7 wherein, for cams of five to eight lobes, saidfirst rectilinear section subtends an angle between 2 and 5 at thecenter of said cam, said curved section subtends an angle of between 7and 9 at said center of said cam and said second rectilinear sectionsubtends an angle between 2 and 5 at said center of said cam.

9. The device of claim 6 wherein said second rectilinear section of saidfirst part of said profile of said cam lobe which extends at leastbetween said point corresponding substantially to the quarter liftposition of said cam follower means and said point corresponding to saidhalf lift position of said cam follower means, has a gradient of between0.5 and 0.3 mm per degree of rotation of said cam.

10. The device of claim 6 wherein said second rectilinear section ofsaid first part of said cam lobe, extending at least between said pointcorresponding substantially to the quarter lift position of said camfollower means and said point corresponding to said half lift positionof said cam follower means, has a gradient arranged so that when saiddevice is used with a pump having a diameter no greater than twice thestroke, will provide a-- theoretical gradient of delivery from said pumpof between 30 mm and 45 mm per degree of rotation of said cam.

ll. The device of claim 1 wherein said two rollers of said cam followermeans are a main roller and a subsidiary roller, and a second part ofsaid profile of each said lobe, extending from the top dead center ofsaid half lift position of said cam follower means, has a convex curvein which the section adjacent said second rectilinear section of saidfirst part of said profile, from said half lift position of said camfollower means to about a three-fourths lift position of said camfollower, has a radius not less than half the diameter of said mainroller of said cam follower means.

112. The device of claim 1 wherein said two rollers of said cam followermeans are a main roller and a subsidiary roller, and a second part ofsaid profile of each said lobe, between top dead center and said halflift position of said cam follower means has a radius of not less thanone-third of said diameter of said main roller of said cam followermeans at the section extending about the position corresponding to thefive-sixths lift position of said cam follower means.

13. The device of claim 1 wherein said two rollers of said cam followermeans are a main roller and a subsidiary roller, and a second section ofsaid profile of each said lobe, between top dead center and saidhalflift position of said cam follower means has a radius of not lessthan one-fourth of said diameter of said main roller said main roller ofsaid cam follower means.

1. A control device for a fuel injection pump of a multicylinderinternal combustion engine, said control device having a casing, a camrotatably mounted in the casing, said cam having a surface including aplurality of lobes, each said lobe being symmetric about a radial linepassing through the top dead center of said lobe, cam follower meanscomprising a rocker arm having at each end thereof a roller, saidrollers both being in contact with the surface of said cam, a supportmember attached to the casing support means on said rocker armcooperating with said support member to support said rocker arm forpivotal movement about an axis intermediate said rollers, said supportmeans being outside the region between said rollers and a connecting rodhaving one end operatively connected to one of said rollers and theother end connected to a cursor slidable in said support members, saidcam surface being shaped such that the part of the profile of each lobeof said cam between the top dead center position and the half liftposition of said cam follower is determined to be the appropriateenvelope of the successive positions of said roller when the other saidroller moves over the part of the profile of said cam between the bottomdead center position and said half lift position of said cam follower.2. The device of claim 1, wherein said rocker arm comprises twoplate-like elements, each said plate-like element having substantiallythe form of an isosceles triangle with rounded vertices and with a baselonger than the sides, a bridge element rigidly connecting saidplate-like eleMents side by side at the vortex opposite said base, saidsupport means including a stub shaft projecting outwardly from each ofsaid plate-like elements, means forming axially aligned apertures ineach pair of the other rounded vertices of the plate-like elements anaxle means for said rollers disposed in said apertures.
 3. The device ofclaim 2 wherein said support member for said rocker arm comprises asubstantially U-shaped element having in each limb thereof a circularaperture of diameter larger than the diameter of each said stub shaft, aslot in each limb of the U-shaped element, each said aperturecommunicating laterally with a respective said slot so as to provide apassage of width at least equal to the diameter of each said stub shaftto allow the radial introduction thereof into said aperture, a bush ineach said aperture having an external diameter equal to the diameter ofthe respective aperture, said bush arranged for insertion into saidaperture over said stub shaft, said bush serving to lock each said stubshaft in position in said aperture.
 4. The device of claim 3 wherein thebase of said U-shaped element has an aperture surrounded by a collarthrough which said cursor passes.
 5. The device of claim 2 wherein thereis provided a bush between each axle for said rollers and the respectiveapertures in the ends of said rocker arm.
 6. The device of claim 1wherein said cam has five or more lobes, and wherein a first part ofsaid profile of each lobe, from the bottom dead center position up tothe point corresponding with the half lift position of said cam followermeans, comprises a concave curve having a radius between 35 and 45 mm,and at least one rectilinear section between said point corresponding tosaid half lift position of said cam follower and said concave curvedsection to which it is tangential, said rectilinear section extending toa point which corresponds substantially to a quarter of the lift of saidcam follower means.
 7. The device of claim 6, wherein said first portionof said profile of each said lobe comprises a first rectilinear section,said concave curved section with radius between 35 and 45 mm, and asecond rectilinear section formed by said rectilinear section extendingto said half lift position of said cam follower means, both of saidrectilinear sections being tangential to said curved section.
 8. Thedevice of claim 7 wherein, for cams of five to eight lobes, said firstrectilinear section subtends an angle between 2* and 5* at the center ofsaid cam, said curved section subtends an angle of between 7* and 9* atsaid center of said cam and said second rectilinear section subtends anangle between 2* and 5* at said center of said cam.
 9. The device ofclaim 6 wherein said second rectilinear section of said first part ofsaid profile of said cam lobe which extends at least between said pointcorresponding substantially to the quarter lift position of said camfollower means and said point corresponding to said half lift positionof said cam follower means, has a gradient of between 0.5 and 0.3 mm perdegree of rotation of said cam.
 10. The device of claim 6 wherein saidsecond rectilinear section of said first part of said cam lobe,extending at least between said point corresponding substantially to thequarter lift position of said cam follower means and said pointcorresponding to said half lift position of said cam follower means, hasa gradient arranged so that when said device is used with a pump havinga diameter no greater than twice the stroke, will provide a theoreticalgradient of delivery from said pump of between 30 mm3 and 45 mm3 perdegree of rotation of said cam.
 11. The device of claim 1 wherein saidtwo rollers of said cam follower means are a main roller and asubsidiary roller, and a second part of said profile of each said lobe,extending from thE top dead center of said half lift position of saidcam follower means, has a convex curve in which the section adjacentsaid second rectilinear section of said first part of said profile, fromsaid half lift position of said cam follower means to about athree-fourths lift position of said cam follower, has a radius not lessthan half the diameter of said main roller of said cam follower means.12. The device of claim 1 wherein said two rollers of said cam followermeans are a main roller and a subsidiary roller, and a second part ofsaid profile of each said lobe, between top dead center and said halflift position of said cam follower means has a radius of not less thanone-third of said diameter of said main roller of said cam followermeans at the section extending about the position corresponding to thefive-sixths lift position of said cam follower means.
 13. The device ofclaim 1 wherein said two rollers of said cam follower means are a mainroller and a subsidiary roller, and a second section of said profile ofeach said lobe, between top dead center and said half lift position ofsaid cam follower means has a radius of not less than one-fourth of saiddiameter of said main roller of said cam follower means at the sectionextending about the position corresponding to nine-tenths lift positionof said cam follower means.
 14. The device of claim 1 where said tworollers of said cam follower means are a main roller and a subsidiaryroller, and the profile of said peak of each said lobe of said cam,about the top dead center position thereof, has a radius not less thanone-fifth of the diameter of said main roller of said cam followermeans.